In the area of safety glass for use in spectacle lenses, lenses for instruments, windows for vehicles, homes, and other applications, laminated structures having one or more layers of optically transparent and flexible plastic materials separating the glass elements have been utilized with the goal of preventing fragmentation and reducing to a minimum the dispersion of splinters when the glass receives an impact of sufficient force to cause breaking. Among the plastic materials applicable for this use, polyurethanes have been proposed as being particularly advantageous.
Thus, British Pat. No. 1,567,394 describes the production of a "double" or preformed two-layer composite sheet with polymers suitable for use in glass-plastic laminates; the double being formed of a layer of a thermoplastic polyurethane exhibiting adhesive characteristics and a second layer of a thermosetting polyurethane. According to this patent, three-ply laminates are prepared consisting of an outside layer of glass to which the aforesaid double or preformed composite sheet is adhesively attached through the medium of the thermoplastic layer.
The British patent notes that the sheet of plastic material can be colored before or after its application against the glass layer, but does not provide any details with regard to the coloring composition or the method for carrying out the coloring.
One method for carrying out the coloring is mentioned in French Pat. No. 2,467,908 where the coloration is obtained through immersion in a bath containing a commercial dye called CIBACRONE, the pH of the bath being less than 4 and preferably on the order of 2.
In addition, the French patent requires that this coloration be carried out at 60.degree. C. or less with colorant concentrations between 0.5-10 grams/liter of bath, preferably 1-3 grams/liter, this coloration treatment capable of being fixed through immersion in a fixing bath, but with no details with regard to conditions. It is clear to the worker of ordinary skill in the art that the use of such a technique poses problems of reproducibility at the industrial level that would be very difficult and burdensome to overcome by technicians and even experts, the maintenance of the level of acidity (pH.ltoreq.4) being practically impossible to obtain in a continuous manner.
A similar structure of a three-layer laminated lens for use in spectacles is described in French Patent Application No. 81 18678, filed Oct. 5, 1981 under the title "Laminated Ophthalmic Glass and Method of Fabrication" (U.S. Application Ser. No. 349,719, filed Feb. 18, 1982), that lens being formed with an outside layer of glass and an inside layer of a thermosetting polyurethane that is optically transparent and which is attached to the glass element through the medium of a thin layer of optically transparent thermoplastic polyurethane. According to that French patent application, the overall thickness of the double or composite plastic sheet is between 0.25-0.55 mm, with a thermoplastic layer having a thickness of 0.04-0.06 mm and a thermosetting layer having a thickness of 0.2-0.5 mm.
In the field of ophthalmic medicine, it has recently become apparent that physical remedies could be applied to certain diseases of the eye which heretofore were considered very difficult to treat, with retention of the faculty of day vision for the patients. Two common examples of these maladies are the following:
(1) "Aphakia"
This malady results from the absence of the crystalline (lens) of the eye, due most often to surgical intervention. Since one of the functions of the lens is the protection of the retina from ultraviolet rays by optical absorption from a wavelength on the order of 420 to 440 nm, it is obvious that any filter device that can serve in place of the missing lens would be an appreciable advantage to the patient.
(2) "Retinitis pigmentosa"
This malady is the result of the alteration, in a first stage, of the "nocturnal" photoreceivers (generally called rods) of the eye. These photoreceivers, generally situated in the perimeter of the retina, are, owing to their sensitivity curve with the maximum lying at 510 nm, responsible for night vision while having little responsibility for color recognition, merely greys and shadows (see, in this connection, the description given in reference to FIG. 1 of the European patent application published Dec. 16, 1981 under No. 41,789).
The "diurnal" photoreceivers of the eye (generally called cones) occupy the center of the retina and have maximum sensitivity around 560-565 nm (see this same FIGURE); they are responsible for day vision and color recognition.
Alteration of these photoreceivers (rods and cones) can be due to the widest variety of causes, such as contusion or mechanical injuries, prolonged accidental irradiation (electric arc, sunlight, etc.), but also bacterial (rarely viral) infection and above all, retinal degeneration.
It is generally admitted that retinal degeneration and bacterial infections of the cones and rods can be considerably inhibited by protecting them from harmful rays. It is, moreover, also acknowledged that the alteration of the rods is much faster than that of the cones. It will thus be easy to understand the great interest there would be in a filter protecting the rods of the eye from harmful rays. But in the matter of their protection, the selection of a filter of ultraviolet radiation should be accompanied by a certain number of precautions such as:
(a) possibility of filtering the light both in the presence and the absence of sunlight; and
(b) possibility of safeguarding the sensitivity of the cones, enabling the patient to retain color recognition and distinction.
Photochromic filter lenses have been proposed by M. L. Wolbarsht and others in "RETINITIS PIGMENTOSA, CLINICAL IMPLICATIONS OF CURRENT RESEARCH", Advances in Experimental Medicine and Biology, 77, pages 181 to 190, Plenum Publishing Corp., New York. To these proposals should be added the said European patent application bearing on a photochromic filter product responding to the medical needs set forth here, but whose application is possible only with certain vitreous compositions. That European patent application requires a surface reducing treatment of certain metallic oxides contained in the basic glass, which treatment results in lenses that have retained their photochromic properties while also exhibiting the requisite filtering properties. Unfortunately, this treatment is applicable only to a limited number of vitreous compositions, viz., those containing easily reducible metal oxides.
The present invention is directed to the coloring of the polyurethane double or composite plastic sheet either before (that is to say in its current state), or after lamination (that is to say after attachment with the glass layer), the second practice being preferred because it is more profitable in the commercial production of the final product. The inventive method is especially useful in ophthalmic applications. Thus, in preparing corrective lenses for eyeglasses, it is common practice to use glasses exhibiting special properties as to refractive index and dispersion; even combinations of several glasses of different refractive indices sealed to one another in a single lens, commonly termed a multi-focal lens. The instant invention provides a method for preparing eyeglass lenses demonstrating filtering properties appropriate to the desires of the ophthalmologist and adjustable according to the degree of evolution of the retinal alteration of the patient due to aphakia or retinitis pigmentosa.
The present invention is more particularly concerned with a method for coloring polyurethane followed by a fixation operation. According to the present invention, the coloring operation is carried out with the aid of a dispersion of colorants in an aqueous solution containing a wetting agent or surfactant. The solution is subjected to constant agitation to improve the dispersion of colorant and to maintain the level of color and homogeneity of the tinted surface. As for the subsequent fixation operation, it is carried out through a thermal treatment and rinsing which requires an open structure in the polyurethane sheet in order to fix the colorant therewithin.
In practice, the simplest method for fixing consists of rinsing in a boiling aqueous solution of sodium alkyl sulfonate a kind known under the designation of "Teepol", for example, at a concentration of 30 cc/liter at 99.degree. C. for less than 10 minutes.
Satisfactory results have been obtained with a product termed "plastosoluble" formed of dispersed colorants having a low solubility in water and which is called thus because, concentrated and prepared in the dispersed state for synthetic fibers of the textile industry, it diffuses and appears to dissolve therein, giving rise to the graphic expression "plastosoluble". For effective application from aqueous liquids, it is convenient to incorporate soluble dispersing agents in the water such as surfactants.
In fact, it is necessary to "microdisperse" the colorant to obtain a stable colloidal solution in the bath of dye and to maintain this microdispersion throughout the whole operation, which factor underscores the importance of the added surfactant to inhibit eventual agglomeration in the course of the operation.
The colorants utilized are of the type currently named A.C.R. in commerce and could be supplied by the New Chemical Technical Society (T.C.N.), 8 Allee Marie-Louise, 92240 Malakoff, France. They are employed for the coloration of other organic materials such as, for example, an alkyl carbonate of diethylene glycol, known under the commercial designation "CR 39". It is worth noting that, if the colorants utilized in the practice of the present invention are of the type as those employed for "CR 39", they do not give rise to the same tints in the two cases; the reason for this situation being the chemical acceptability of polyurethane colored according to the process of the present invention.
Furthermore, the choice of coloring materials utilized to obtain the stated proper tint and of the surfactant is made from products of commerce on the basis of profit making capability and not as a limitation of the present invention.